Modern large-scale telecommunications electronics systems or mainframe computing systems typically comprise shelves of modules for processing, data exchange or memory storage. These modules are interconnected by means of a large printed circuit board (PCB), known as a backplane, placed in the back of a cabinet in which the shelves reside. In a traditional architecture, the individual modules are plugged into the backplane via hardware point-to-multipoint interconnects.
The quest for greater interconnect throughput has resulted in the need for the backplane to carry lines running at upwards of 1 gigabit per second (Gbps). However, at such rates, the use of conventional hardwired interconnects is not feasible due to the fact that they cannot be terminated in the line characteristic impedance. Furthermore, reliability requirements favour isolation among modules so that catastrophic failure of one module does not affect the others.
These ever more demanding requirements of speed and reliability have spawned the development of what are known in the data transmission field as non-contact (or "AC") buses and backplanes, a discussion of which can be found in U.S. Pat. No. 3,619,504 (De Veer et al.), incorporated by reference herein. In a system employing non-contact technology, a main signal trace carries a data signal and a number of substantially identical couplers are placed in a row along the main signal trace.
More specifically, each of the substantially identical couplers has a conductive track of a given length placed in parallel to the main signal trace. As electrical pulses from a signal driver travel along the main signal trace, electric and magnetic fields are induced in the track of each coupler, causing the generation of a backwards pulse in each coupler that is picked up by a respective receiver.
In an ideal non-contact system, the signals being induced in each coupler should have the same strength. However, a fraction of the energy of a data pulse is lost as it couples into each subsequent coupler. Furthermore, at frequencies exceeding 1 GHz loss due to the transmission line itself can be significant. Therefore, the last coupler receives a significantly weaker signal than the first coupler, resulting in a large disparity in the voltages that are received by the receivers connected to the various couplers. The receivers used in current non-contact coupling systems must therefore support a wide dynamic range, inconveniently leading to a high overall system cost.